Sarcopenia, or the deterioration of muscle health with advancing age, is a major public health concern in the developed world. Some of the most important factors underlying the development of sarcopenia are age- related change in muscle composition, including the replacement of muscle fibers by fat and the loss of muscle force production. Declines in muscle composition and muscle force with aging are predictive of incident mobility limitations. Fortunately, both pharmacologic and exercise interventions hold the prospect of forestalling or even reversing this seemingly inexorable process. However, to date, identifying and monitoring these changes in muscle require the use of inconvenient technologies, including quantitative computerized tomography (QCT) and magnetic resonance imaging (MRI) of muscle to evaluate muscle composition or measures of muscle force production that are either insensitive to small changes or clinically inappropriate for wide use among older adults. None of these assessment methods can be self-administered. A new measure that could be easily utilized by both clinicians and patients and that could provide ongoing assessment of muscle health and the impact of exercise and pharmacologic interventions could find wide application. Electrical impedance myography (EIM) is a technique that could serve this purpose. EIM is already finding use in neuromuscular disease evaluation, including in muscle diseases and amyotrophic lateral sclerosis. Convergence Medical Devices, Inc. is a small business concern that is focused on the development and commercialization of EIM systems. It has developed an initial prototype system now being deployed in neuromuscular disease clinical trials and has also gathered substantial preliminary data among older adults. In this Phase 1 application, we will assess EIM's potential value as a tool for the self-assessment of muscle composition such that it could ultimately serve as an at-home measuring and motivational tool. Our central hypothesis is that EIM is sensitive to changes in muscle health that underlie sarcopenia, and given its ease of use, EIM can be employed as a convenient tool to monitor exercise and pharmacologic interventions. We assess this hypothesis through three specific aims. In Aim 1, we will pursue software modifications to make the current EIM system easier to use by older adults with minimal computer expertise and with functional/visual limitations. In Aim 2, an experienced evaluator will perform EIM measurements on 2 upper and 3 lower extremity muscles among 60 older adults. After a brief training session, the subjects themselves will also be asked to make the same measurements and the reliability of self-assessment will be determined. In Aim 3, we will determine the relationship between EIM data and measures of muscle composition (via quantitative computer tomography) and muscle force (leg strength and leg power) in these 60 individuals, to determine whether EIM measurements can serve as clinically relevant surrogates for some or all of these muscle health parameters within a multivariable model predicting mobility performance. Upon successful completion of these 3 aims, we will be well poised to pursue a Phase 2 STTR project geared toward developing and validating a small, inexpensive EIM device for home use. In that study, we will employ this EIM device in a study of at-home, self-assessment of muscle health during an extended exercise and/or drug intervention targeting sarcopenia and physical functioning.